The Internet Protocol (IP) Multimedia Core Network Subsystem (IMS), which is brought forward by the 3rd Generation Partnership Project (3GPP), is a network architecture based on IP. The IMS has built an open and flexible service setting, supports multimedia application, and provides abundant multimedia services for users.
The IMS is a telecommunication network architecture based on IP, and is not related to the access technique. The IMS can not only provide services for Packet Switching (PS) assess networks such as General Packet Radio Service (GPRS), Wireless Local Area Network (WLAN) etc., but can also provide services for mobile cellular networks such as Global System for Mobile communications (GSM), Universal Mobile Telecommunications System (UMTS), etc.
The mobile cellular networks, such as GSM, UMTS, etc., apply circuit switched techniques, referred to as Circuit Switched (CS) domain, and can provide basic voice services and supplement services based on the voice services for users. When the CS domain accesses the IMS, the CS domain evolves into an access means and the services are solely provided by the IMS uniformly. This technique is called IMS Centralized Service (ICS).
FIG. 1 is a schematic diagram illustrating the framework of the access of a non ICS UE (an ordinary UE without the ICS service capability) under an enhanced network of the IMS centralized control service, involving the following network elements:
101, a User Equipment (UE);
102, an Enhanced Mobile Switch Center (eMSC);
103, a Media Gateway (MGW);
104, a Call Session Control Function (CSCF);
105, a conferencing server, which includes an Application Server (AS), a Multimedia Resource Function Controller (MRFC) and a Multimedia Resource Function Processor (MRFP);
106, a Home Subscriber Server (HSS), storing subscriber data of the CS domain and the IMS domain.
The enhanced MSC server 102 is an enhancement of a CS domain MSC server. Besides implementing access and mobile management of CS user equipments, the enhanced MSC server 102 also serves as a Session Initiation Protocol (SIP) user agent to implement transformation between CS signaling and SIP signaling and access an IMS instead of the user.
The user equipment 101 accesses the enhanced MSC server 102 by CS control signaling. The enhanced MSC server 102 serves as a user agent to access the IMS network instead of the CS user equipment 101 and set up a session connection with a remote user. Meanwhile, the MGW103 accomplishes the transformation between a media stream on a CS bearer and a media stream on an IP bearer and sets up a media connection between the user equipment 101 and the remote user. Wherein, the Session Initiation Protocol is used between the enhanced MSC server 102 and the CSCF 104 in the IMS network, and the conferencing server 105 in the IMS network provides services related to a conference.
FIG. 2 is a flow chart of an IMS conference service. A UE-A sets up a call with a UE-B, the UE-A keeps this session, and then the UE-A sets up a session with a UE-C and enters a call state. At this moment, the UE-A serves as the chairman of the conference and decides to add the two sessions into the conference, and implements following steps:
201, the UE-A creates a conference, and originates a session request message to a conferencing server according to the address of the conferencing server stored by itself; the message arrives at the conferencing server through a CSCF;
202, the conferencing server returns a success response to the UE-A through the CSCF, thus a bearer connection between the UE-A and the conferencing server is set up.
203, the UE-A instructs the UE-B to participate in the conference;
204, the UE-A instructs the UE-C to participate in the conference, thus a tripartite conferencing call is set up successfully.
Under the architecture shown in FIG. 1, the access of the non ICS UE has not realized the conference service of the IMS centralized control service. Besides, if the eMSC should simulate an IMS UE to carry out the conference service instead of the non ICS UE, the eMSC could not know the address of the conferencing server. Thus how to implement a conference service of the IMS centralized control service after the access of a non ICS UE serving as a chairman is a problem to be solved.